MICROSTRUCTURE OF THERMOELECTRIC SIGE ALLOYS CONTAINING FULLERITE

A series of thermoelectric materials has been characterized microstruc turally. The materials are Si80Ge20 (at.%) alloys with additions of fu llerite in the concentrations 0, 0.2 and 2.0 wt.%. The alloys were fab ricated by a hot sintering technique, where the feed power was produce d by mechanical alloying (MA). Fullerite was added either before or af ter MA. The experimental results have demonstrated that a high density of microtwins, some of them a few nanometers thick, exists in the all oys. The number density of the microtwins has been found to be over 10 (8) cm(-2). The addition of fullerite greatly reduced the grain size o f the hot sintered alloys. The alloy without fullerite has a grain siz e of between 0.5 and 5 mu m, whereas the grain size of the alloy with 2.0 wt% fullerite is decreased by one order of magnitude. Owing to a f ine gain structure, the dislocation density in the alloy with fullerit e is much less than 10(9) cm(-2). It has also been found that the adde d fullerite reacted with the surrounding SiGe matrix to produce an f.c .c. silicon carbide of lattice parameter 0.4359 nm. It is concluded fr om analysis of Moire fringes that the interface between the small SiC particles and the matrix is not coherent.